1. Field of the Invention
The present invention relates to a method of recording information in an information storage medium, and more particularly, to a method of recording digital data in an optical disk by forming marks on the optical disk.
2. Description of the Related Art
Optical disks onto which data can be recorded, from which data can be erased, and from which data can be reproduced, include 650 MB capacity CD-R and CD-RW disks, as well as 4.7 GB capacity DVD-RAM, DVD-R, DVD-RW, DVD+R, and DVD+RW disks, etc. Also, high-definition DVD (HD-DVD) disks, Blu-ray disks (BDs), etc, whose recording capacities are above 23 GB, are being developed. When data is recorded in such recordable disks, the data is recorded using a recording pulse signal as illustrated in FIG. 1.
Referring to FIG. 1, if a recording time unit is T and a recording pulse signal corresponds to N times the recording time unit T, the recording pulse signal consists of N-1 recording pulses. Additionally, parameters for constructing the N-1 recording pulses must be optimized. In other words, in an example illustrated in FIG. 1, since the quality of a recording signal waveform that is to be used in the recording of data depends on several parameters, it is necessary to set these parameters to optimal values in order to produce high-quality recordings on the disks. The recording parameters include a power level of a record pattern (Pw), a power level of an erase power (Pe), an offset between the beginning of the mark and the beginning of the record pattern (dTop), a length (a time width) of a top pulse of a pulse train within the record pattern (Ttop), a length (a time width) of each pulse in the multipulse (Tmp), a bias power level (Pb), and an offset between the end of the record pattern and the beginning of the erase pattern (dTe).
In order to optimize these parameters, a method of setting the parameters to different values according to lengths of marks to be recorded is generally used. For example, if the seven parameters to be used in the recording are Pw(n), Pe(n), dTtop(n), Ttop(n), Tmp(n), Pb(n), and dTe(n) when a mark having a length nT (T is a unit length) is recorded, the 7 parameters are optimized according to possible run-length conditions. For example, in the case of a DVD, since run-length conditions are 3 T-11 T and 14 T, optimal parameter values have to be set from parameter values (Pw(3), Pe(3), dTtop(3), Ttop(3), Tmp(3), Pb(3), and dTe(3)) which correspond to the run-length condition of 3 T, to parameter values (Pw(14), Pe(14), dTtop(14), Ttop(14), Tmp(14), Pb(14), and dTe(14)) that correspond to the run-length condition of 14 T. However, for parameter values which correspond to the run-length condition 12 T and 13 T are not set because they are not run-length conditions of the DVD.
A typical set of write strategy condition (WSC(n)) of 7 parameters with respect to nT can be defined as Equation 1 below.WSC(n)={Pw(n),Pe(n), dTtop(n),Ttop(n),Tmp(n),Pb(n),dTe(n)}  (Equation 1)
If the number of recording parameters varies, the number of elements of the set WSC(n) will also vary. Recently, a lot of research on methods to optimize the parameters has been conducted. For example, one of the parameter optimization methods has the parameter set WSC(n) defined only in correspondence to run-length conditions. For example, in the case of a CD, since run-length conditions are 3 T-11 T only WSC(3) through WSC(11) are defined. In the case of a DVD, since run-length conditions are 3 T-11 T and 14 T, only WSC(3) through WSC(11) and WSC(14) are defined. Also, in the case of a BD, since run-length conditions are 2 T-9 T, only WSC(2) through WSC(9) are defined.
However, it has been found by experimentation that, when different run-length conditions are set according to not only a mark signal, but to run-lengths of spaces ahead of and behind the mark signal, a signal with higher quality can be obtained as data is recorded according to the different run-length conditions.
In more detail, in the case of a parameter set as WSC(5) for recording a current mark corresponding to 5 T, the parameter values of the WSC(5) are defined as different values, respectively, when a space ahead of the current mark of 5 T has a length of 3 T, 4 T, 5 T, and so on, and are also defined as different values, respectively, when a space behind the current mark of 5 T has a length of 3 T, 4 T, 5 T, and so on. For example, in a BD, in a parameter set WSC(5) for recording a current mark corresponding to 5 T, since a space ahead of the current mark of 5 T can have a length from 2 T to 9 T, 8 cases are possible. Also, since a space behind the current mark of 5 T can have a length from 2 T to 9 T, 8 cases are further possible. Accordingly, a signal waveform of the WSC(5) will be optimized according to a total of 64 (=8×8) cases.
Accordingly, Equation 1 can be rewritten for the BD as Equation 2 below.
                              WSC          ⁡                      (                          nprev              ,              n              ,              nnext                        )                          =                              {                                          Pw                ⁡                                  (                                      nprev                    ,                    n                    ,                    nnext                                    )                                            ,                              Pe                ⁡                                  (                                      nprev                    ,                    n                    ,                    nnext                                    )                                            ,                              Ttop                ⁡                                  (                                      nprev                    ,                    n                    ,                    nnext                                    )                                            ,                              Ttop                ⁡                                  (                                      nprev                    ,                    n                    ,                    nnext                                    )                                            ,                              Tmp                ⁡                                  (                                      nprev                    ,                    n                    ,                    nnext                                    )                                            ,                              Pb                ⁡                                  (                                      nprev                    ,                    n                    ,                    nnext                                    )                                            ,                              dTe                ⁡                                  (                                      nprev                    ,                    n                    ,                    nnext                                    )                                                      }                    .                                    (                  Equation          ⁢                                          ⁢          2                )            
Here, nprev denotes a run-length of a space ahead of a current mark, and nnext denotes a run-length of a space behind the current mark. For example, the case where a space of 3 T exists ahead of a mark of 5 T, and a space of 6 T exists behind the mark of 5 T can be expressed as WSC(3,5,6). In the case of a BD, since both the run-length of a space ahead of a current mark and the run-length of a space behind the current mark can be defined as a length from 2 T to 9 T, the number of cases for recording the current mark becomes 512 (=8×8×8).
As recording density increases, the lengths of marks and spaces that are to be recorded decrease with respect to the diameter of a laser beam. Accordingly, it is necessary to further consider the influences of adjacent signals, such as spaces which are located two or more spaces ahead of and behind a mark that is to be recorded, as well as spaces just ahead of and behind the corresponding mark. Thus, the number of cases to consider in optimizing the signal waveform increases exponentially, and requires much resource to construct a system that can handle the large amount of cases.